The present disclosure relates to the fields of mechanical ventilation and respiratory support. More specifically, the present disclosure relates to a method of evaluating a patient for positive end expiratory pressure (PEEP) therapy.
Mechanical ventilation is a commonly accepted medical practice in the treatment of individuals experiencing respiratory problems. The patient may be too weak from disease and/or sedation from an anesthetic agent to complete an entire respiratory cycle under his own power. In these instances, mechanical ventilatory assistance is provided whereby patient's spontaneous breath attempts are detected by the ventilator and respiratory assistance is provided accordingly.
One specific form of respiratory therapy is the application of a positive and expiratory pressure (PEEP). During mechanical ventilation with (or without) PEEP, the patient is allowed to exhale naturally. The patient's natural exhalation is a function of the compliance and resistance of the patient's lungs. When an inspiratory pressure from the mechanical ventilator is terminated, the lungs return to a natural equilibrium state, forcing inspired air out of the lungs. PEEP therapy applies an external pressure to the lungs to maintain an elevated airway pressure reaching a new equilibrium state at a higher lung volume than without PEEP.
As a patient exhales, the pressure in the lungs drops until it approaches airway pressure. As the pressure within the lungs drops, the alveoli, or air sacs, in the lungs deflate. If alveolar sacs collapse completely, more pressure is required upon inspiration to reach the opening pressure and re-inflate the alveolar sacs. By applying PEEP, the additional pressure in the patient's lungs keeps more of these alveolar sacs from completely collapsing upon expiration and, as such, allows them to participate in ventilation. This decreases the relative pressure change required to re-inflate the lung and further increases the end expiratory lung volume (EELV) of the patient.
There are two components to the increased EELV as PEEP is increased. One component is due to the stretching of the lung by the increased pressure. A second, more desirable component, occurs from “recruiting” alveolar sacs by preventing their collapse upon exhalation, as described above.
The EELV component due to stretching, or distension, of the lungs is associated with a variety of risks to the patient. Excessive lung distension can cause compression of the pulmonary bed of the lung, loading on the right side of the heart, reducing blood volume available for gas exchange, as well as volutrautomatic damage to the lungs themselves.